The present invention relates to a propellant composition, and particularly to a propellant composition containing copolyurethane thermoplastic elastomers.
In the last decade, there has been a significant interest to develop an improved low vulnerability gun propellant (LOVA) formulation for use in insensitive munitions (IM).
A LOVA gun propellant is one which burns properly when intentionally ignited, but which shows low insensitivity towards unplanned external stimuli such as shock or fire. Although most LOVA formulations of the first generation serve well their purposes, they cannot withstand extreme weather conditions where the propellant is subjected to very low temperature, less than xe2x88x9220xc2x0 C. In cold weather, the first generation of LOVA formulations as well as the conventional gun propellant formulations loose their mechanical integrity as the gun propellant grains become brittle and crack, which can cause overpressures in the gun barrels leading to breech bursts. Moreover, gun cartridges filled with brittle grains are more sensitive to external stimuli. Hence, they can provoke catastrophic accidents as well as erratic ballistics.
A directive of one embodiment of the present invention is to provide propellant compositions which are capable of exhibiting good mechanical behavior under cold weather.
Propellant compositions commonly include energetic copolyurethane thermoplastic elastomer (TPE). Thermoplastic elastomers typically consist of copolymer chains having monomers A and B distributed throughout the chains as ABA or AB, where the A is the hard segment providing the thermoplastic characteristic and B is the soft segment providing the elastomeric behavior to the polymer. Conventionally, the A segment is formed by a crystalline homopolymer and the soft segment is formed by an amorphous homopolymer.
Thermoplastic elastomers of the type ABA are usually obtained by polymerization the soft B segment followed by the addition of the hard A segment, which is crystallisable. To achieve this type of copolymerization, monomers of both types should have similar reactivity to provide a copolymer of controlled structure with suitable adjustable mechanical properties. A good example of this type of technology is the preparation of 3-azidomethyl-3-methyloxetane and 3.3-bis(azidomethyl)oxetane (AMMO/BAMO) energetic thermoplastic elastomer described in U.S. Pat. No. 4,707,540, issued to Manser et al., Nov. 17, 1987 and U.S. Pat. No. 4,952,644, issued to Wardle et al., Aug. 28, 1990. In this energetic thermoplastic elastomer (ETPE), the thermoplastic part is obtained by the crystallization of the BAMO polymer. Manser et al. also described the use of these AMMO/BAMO energetic homopolymers as prepolymers in making thermoset binders for use in propellants. To obtain the thermoset binders, Manser et al. would typically cure the AMMO/BAMO prepolymers with a triol and diisocyanate to form a chemically cross-linked matrix to obtain the desired binder.
In the case of copolymers of the type AB, the thermoplastic elastomers are usually obtained by mixing monomers that have compatible reactive ending groups. U.S. Pat. No. 4,806,613, to Wardle, Feb. 21, 1989, describes such a method of synthesis. Similarly to Manser et al., Wardle also uses BAMO as the crystalline hard segment. In this, both the A and B homopolymers were end capped with toluene diisocyanate (TDI) leaving at each end an unreacted isocyanate. The homopolymers were mixed and joined by using a small chain extender. Alternatively, Wardle used a block linking technique consisting of reacting the B block with phosgene or a diisocyanate followed by the addition of the A block to form the thermoplastic elastomer. Once again, the crystalline homopolymer BAMO which is an expensive starting material is required to form the hard segment of the thermoplastic elastomer. Moreover, this type of thermoplastic elastomer is not recyclable. Hence the use thereof in a gun propellant would produce a propellant that is expensive to make and non-recyclable. Therefore, there exists a need for a gun propellant that is inexpensive and recyclable.
One object of one embodiment of the present invention is to provide propellant compositions which are useful in cold weather and which incorporate thermoplastic elastomers having copolymer chains with urethane moieties physically bonded by hydrogen bonds to yield the hard segment of the thermoplastic elastomer.
A further object of one embodiment of the present invention is to provide a propellant composition comprising an energetic copolyurethane thermoplastic elastomer, the thermoplastic elastomer including a hard segment generated by the formation of hydrogen bonds between a first urethane group of one linear copolymer chain with a second urethane group of another linear copolymer chain.
Preferably, the amount of energetic copolyurethane thermoplastic elastomer in the propellant composition of the present invention ranges from about 7 to about 15 weight percent, and most preferably, it is in an amount of about 9 weight percent.
Yet another object of one embodiment of the present invention is to provide a propellant composition comprising:
(a) between 70 and 85 weight percent of an explosive crystal;
(b) between 0 and 6 weight percent of an inert binder;
(c) between 7 and 15 weight percent of an energetic copolyurethane thermoplastic elastomer; the thermoplastic elastomer including a member selected from the group comprising:
(i) a hard segment generated by the formation of hydrogen bonds between a first urethane group of one linear copolymer chain with a second urethane group of another linear copolymer chain;
(ii) a linear copolymer chain comprising an A block and a B block, the copolymer chain having the formula:
HOxe2x80x94Pxe2x80x94(Uxe2x80x94P)nxe2x80x94OH
wherein P is selected from the group consisting of 
where the R1 groups are the same and selected from the group consisting of xe2x80x94CH2N3 and xe2x80x94CH2ONO2;
R2 is selected from the group consisting of xe2x80x94OCH2CH2Oxe2x80x94, xe2x80x94OCH2CH2CH2Oxe2x80x94 and xe2x80x94OCH2CH2CH2CH2Oxe2x80x94 and o and p are each greater than 1; and 
where the R3groups are the same and selected from the group consisting of xe2x80x94CH2N3 and xe2x80x94CH2ONO2;
the R4 groups are xe2x80x94CH3;
R5 selected from the group consisting of xe2x80x94OCH2CH2Oxe2x80x94, xe2x80x94OCH2CH2Oxe2x80x94 and xe2x80x94OCH2CH2CH2Oxe2x80x94; and q and r are both less than 1;
U is selected from the group consisting of 
and n is 1 to 100;
wherein the A block is provided by the U moieties and the B block is provided by the P moieties.
(iii) a linear copolymer chain comprising an A block and a B block, the copolymer chain having the formula:
HOxe2x80x94Pxe2x80x94(Uxe2x80x94(Cxe2x80x94U)axe2x80x94P)bxe2x80x94Uxe2x80x94Pxe2x80x94OH
wherein P is selected from the group consisting of 
where the R1 groups are the same and selected from the group consisting of xe2x80x94CH2N3 and xe2x80x94CH2ONO2;
R2 is selected from the group consisting of xe2x80x94OCH2CH2Oxe2x80x94, xe2x80x94OCH2CH2CH2Oxe2x80x94 and xe2x80x94OCH2CH2CH2CH2Oxe2x80x94; and o and p are each greater than 1; and 
where the R3 groups are the same and selected from the group consisting of xe2x80x94CH2N3 and xe2x80x94CH2ONO2;
the R4 groups are xe2x80x94CH3;
R5 is selected from the group consisting of xe2x80x94OCH2CH2Oxe2x80x94, xe2x80x94OCH2CH2CH2Oxe2x80x94 and xe2x80x94OCH2CH2CH2CH2Oxe2x80x94; and q and r are both greater than 1;
U is selected from the group consisting of 
C is selected from the group consisting of 
xe2x80x83and
xe2x80x94OCH2xe2x80x94(CH2)nxe2x80x94CH2Oxe2x80x94 where n is 0 to 8;
a is 1 to 100 and b is 1 to 100;
wherein the A block is provided by the U moieties and the B block is provided by the P moieties.
(iv) a linear copolymer chain comprising an A segment and a B segment, the copolymer chain having the formula:
HOxe2x80x94Pxe2x80x94Uxe2x80x94(Cxe2x80x94U)xxe2x80x94(Pxe2x80x94U)yxe2x80x94(Cxe2x80x94U)zxe2x80x94Pxe2x80x94OH
wherein P is selected from the group consisting of 
where the R1 groups are the same and selected from the group consisting of xe2x80x94CH2N3 and xe2x80x94CH2ONO2;
R2 is selected from the group consisting of xe2x80x94OCH2CH2Oxe2x80x94; xe2x80x94OCH2CH2CH2xe2x80x94 and xe2x80x94OCH2CH2CH2CH2Oxe2x80x94; and o and p are each greater than 1; 
where R3 groups are the same and selected from the group consisting of xe2x80x94CH2N3 and xe2x80x94CH2ONO2;
the groups are xe2x80x94CH3;
R5 is selected from the group consisting of xe2x80x94OCH2CH2Oxe2x80x94, xe2x80x94OCH2CH2Oxe2x80x94 and xe2x80x94OCH2CH2CH2Oxe2x80x94; and q and r are both  greater than 1;
U is selected from the group consisting of 
C is selected from the group consisting of 
xe2x80x83and
xe2x80x94OCH2xe2x80x94(CH2)nxe2x80x94CH2Oxe2x80x94 where n is 0 to 8;
x, y and z are each an integer from 1 to 100;
wherein the A segment is provided by the U moieties and the B segment is provided by the moieties.
(d) between 4 and 10 weight percent of a plasticizer;
(e) between 0 and 8 weight percent of nitrocellulose; and
(f) between 0 and 1 weight percent of a stabilizer.
The energetic copolyurethane TPE is admixed in a matrix to form the propellant composition of the present invention. The preferred matrix system contains explosive crystals, for example, nitramines such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), in an amount from about 70 to about 85 weight percent and a plasticizer in an amount from about 4 to about 10 weight percent. Suitable plasticizers are energetic plasticizers, for example, nitrate esters such as triethylene glycol dinitrate (TEGDN), 1,1,1-trimethylethane trinitrate (TMETN) or bis-(2,2-dinitropropyl acetal/formal (BDNPA/F), or inert plasticizers.
Additional ingredients which may be included in the formulation are nitrocellulose in an amount of about 0 to about 8 weight percent, an inert binder, for example, cellulose acetate butyrate, in an amount of from about 0 to about 6 weight percent and a stabilizer such as ethyl centralite in an amount of from about 0 to about 1 weight percent.
A still further object of one embodiment of the present invention is to provide a propellant composition, comprising a thermoplastic elastomer, the elastomer comprising a linear copolymer chain comprising an A block and a B block, the copolymer chain having the formula:
HOxe2x80x94Pxe2x80x94(Uxe2x80x94P)nxe2x80x94OH
wherein P is selected from the group consisting of 
where the R1 groups are the same and selected from the group consisting of xe2x80x94CH2N3 and xe2x80x94CH2ONO2;
R2 is selected from the group consisting of xe2x80x94OCH2CH2Oxe2x80x94, xe2x80x94OCH2CH2CH2Oxe2x80x94 and xe2x80x94OCH2CH2CH2CH2Oxe2x80x94; and o and p are each greater than 1; and 
where the R3 groups are the same and selected from the group consisting of xe2x80x94CH2N3 and xe2x80x94CH2ONO2;
the R4 groups are xe2x80x94CH3;
R5 is selected from the group consisting of xe2x80x94OCH2CH2Oxe2x80x94, xe2x80x94OCH2CH2CH2Oxe2x80x94 and xe2x80x94OCH2CH2CH2CH2Oxe2x80x94; and q and r are both greater than 1;
U is selected from the group consisting of 
and n is 1 to 100;
wherein the A block is provided by the U moieties and the B block is provided by the P moieties.
In one embodiment of the present invention, the propellant composition includes about 77 weight percent of the explosive crystals, about 2 weight percent of the inert binder, about 9 weight percent of the energetic copolyurethane thermoplastic elastomer, about 7.6 weight percent of the plasticizer, about 4 weight percent of the nitrocellulose and about 0.4 weight percent of the stabilizer.
Another object of one embodiment of the present invention is to provide a propellant composition, comprising a thermoplastic elastomer, the elastomer, comprising a linear copolymer chain comprising an A block and a B block, the copolymer chain having the formula:
HOxe2x80x94Pxe2x80x94(Uxe2x80x94(Cxe2x80x94U)axe2x80x94P)bxe2x80x94Uxe2x80x94Pxe2x80x94OH
wherein P is selected from the group consisting of 
where the R1 groups are the same and selected from the group consisting of xe2x80x94CH2N3 and xe2x80x94CH2ONO2;
R2 is selected from the group consisting of xe2x80x94OCH2CH2Oxe2x80x94, xe2x80x94OCH2CH2CH2Oxe2x80x94 and xe2x80x94OCH2CH2CH2CH2Oxe2x80x94; and o and p are each greater than 1; and 
where the R3 groups are the same and selected from the group consisting of xe2x80x94CH2N3 and xe2x80x94CH2ONO2;
the R4 groups are xe2x80x94CH3;
R5 is selected from the group consisting of xe2x80x94OCH2CH2Oxe2x80x94, xe2x80x94OCH2CH2CH2Oxe2x80x94 and xe2x80x94OCH2CH2CH2CH2Oxe2x80x94; and q and r are both greater than 1;
U is selected from the group consisting of 
C is selected from the group consisting of 
xe2x80x83and
xe2x80x94OCH2xe2x80x94(CH2)nxe2x80x94CH2Oxe2x80x94 where n is 0 to 8;
a is 1 to 100 and b is 1 to 100;
wherein the A block is provided by the U moieties and the B block is provided by the P moieties.
The propellant composition of the present invention is useful as, for example, a gun or rocket propellant, an explosive, a pyrotechnic or can be incorporated in gas generators for air bags in the car industry.
A further object of one embodiment of the present invention is to provide a propellant composition, comprising a thermoplastic elastomer, the elastomer, comprising a linear copolymer chain comprising an A segment and a B segment, the copolymer chain having the formula:
HOxe2x80x94Pxe2x80x94Uxe2x80x94(Cxe2x80x94U)xxe2x80x94(Pxe2x80x94U)yxe2x80x94(Cxe2x80x94U)zxe2x80x94Pxe2x80x94OH
wherein P is selected from the group consisting of 
where the R1 groups are the same and selected from the group consisting of xe2x80x94CH2N3 and xe2x80x94CH2ONO2;
R2 is selected from the group consisting of xe2x80x94OCH2CH2Oxe2x80x94, xe2x80x94OCH2CH2CH2Oxe2x80x94 and xe2x80x94OCH2CH2CH2CH2Oxe2x80x94; and o and p are each greater than 1; and 
where the R3 groups are the same and selected from the group consisting of xe2x80x94CH2N3 and xe2x80x94CH2ONO2;
the R4 groups are xe2x80x94CH3;
R5 is selected from the group consisting of xe2x80x94OCH2CH2Oxe2x80x94, xe2x80x94OCH2CH2CH2Oxe2x80x94 and xe2x80x94OCH2CH2CH2CH2Oxe2x80x94; and q and r are bothxe2x89xa71;
U is selected from the group consisting of 
and
C is selected from the group consisting of 
xe2x80x83and
xe2x80x94OCH2xe2x80x94(CH2)nxe2x80x94CH2Oxe2x80x94 where n is 0 to 8;
x, y and z are each an integer from 1 to 100;
wherein the A segment is provided by the U moieties and the B segment is provided by the P moieties.
The advantages of the propellant composition of the present invention are to provide a propellant which can withstand cold temperature, has a high energy content and is recyclable. The propellant composition of the present invention have an energy level above 1200 J/g, which is a noticeable improvement from prior art propellants.
Preface
As used herein, the terms xe2x80x9cGAPxe2x80x9d means glycidyl azide polymer; xe2x80x9cGAP1000xe2x80x9d means glycidyl azide polymer of molecular weight 1000; xe2x80x9cETPE-GAP1000xe2x80x9d means an energetic copolyurethane thermoplastic elastomer based on glycidyl azide polymers of molecular weight of 1000; PECH means polyepichlorohydrin; PECH1000 means polyepichlorohydrin of molecular weight 1000.